Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of both gaseous and solid material, such as, for example, particulate matter. Particulate matter may include ash and unburned carbon particles called soot.
Due to increased environmental concerns, exhaust emission standards have become more stringent. The amount of particulate matter and gaseous pollutants emitted from an engine may be regulated depending on the type, size, and/or class of engine. In order to meet these emissions standards, engine manufacturers have pursued improvements in several different engine technologies, such as fuel injection, engine management, and air induction, to name a few. In addition, engine manufacturers have developed devices for treatment of engine exhaust after it leaves the engine.
Engine manufacturers have employed exhaust treatment devices called particulate traps to remove the particulate matter from the exhaust flow of an engine. A particulate trap may include a filter designed to trap particulate matter. The use of the particulate trap for extended periods of time, however, may enable particulate matter to accumulate on the filter, thereby causing damage to the filter and/or a decline in engine performance.
One method of restoring the performance of a particulate trap may include regeneration. Regeneration of a particulate trap filter system may be accomplished by thermal regeneration, which may include periodically increasing the temperature of the filter, and the trapped particulate matter in the filter, above the combustion temperature of the particulate matter, thereby burning away the collected particulate matter and regenerating the filter system. This increase in temperature may be effectuated by various means. For example, some systems employ a heating system (e.g., an electric heating element) to directly heat one or more portions of the particulate trap (e.g., the filter material or the external housing). Other systems have been configured to heat the exhaust gases upstream from the particulate trap, allowing the flow of the heated gases through the particulate trap to transfer heat to the particulate trap. For example, some systems may alter one or more engine operating parameters, such as air/fuel mixture, to produce exhaust gases with an elevated temperature. Other systems heat the exhaust gases upstream from the particulate trap, with the use of a burner that creates a flame within the exhaust conduit leading to the particulate trap.
In addition to particulate traps, exhaust systems may also include other types of after-treatment devices, such as catalyst-based devices. Catalyst-based devices, such as oxidation or reduction catalysts, may be utilized to convert (e.g., via oxidation or reduction) one or more gaseous constituents of an exhaust stream to a more environmentally friendly gas and/or compound to be discharged into the atmosphere. Such catalytic conversion reactions often occur more efficiently above a particular temperature and/or within a particular temperature range. During some situations, such as cold start or idle, an engine may not produce exhaust gases hot enough to maintain the catalyst above the particular temperature or within the desired temperature range. The same types of heating systems discussed above with regard to thermal regeneration have been used in some exhaust treatment systems to maintain the temperature of a catalyst-based device within a desired temperature range to promote favorable conversion efficiency. For example, one such system is disclosed by U.S. Pat. No. 5,771,683 issued to Webb on Jun. 30, 1998 (“the '683 patent”). The '683 patent discloses an exhaust treatment system including a burner device configured to heat a catalyst or, in the case of diesel engines, a particulate trap. However, the system of the '683 patent does not disclose a system including a heating device or system configured to both heat a catalyst, thus maintaining it above a predetermined temperature, and heat a particulate trap in order to effectuate regeneration. Therefore, the '683 patent does not provide an exhaust treatment system capable of controlling a heating system to perform multiple functions. As such, the '683 patent is limited to enhancing either one type of exhaust treatment or another, but not both.
The present disclosure is directed to solving one or more of the problems discussed above.